The present invention generally relates to dermal filler compositions, and more specifically relates to injectable dermal filler compositions including antioxidants.
Skin aging is a progressive phenomenon, occurs over time and can be affected by lifestyle factors, such as alcohol consumption, tobacco and sun exposure. Aging of the facial skin can be characterized by atrophy, slackening, and fattening. Atrophy corresponds to a massive reduction of the thickness of skin tissue. Slackening of the subcutaneous tissues leads to an excess of skin and ptosis and leads to the appearance of drooping cheeks and eye lids. Fattening refers to an increase in excess weight by swelling of the bottom of the face and neck. These changes are typically associated with dryness, loss of elasticity, and rough texture.
Hyaluronan, also known as hyaluronic acid (HA) is a non-sulfated glycosaminoglycan that is distributed widely throughout the human body in connective, epithelial, and neural tissues. Hyaluronan is abundant in the different layers of the skin, where it has multiple functions such as, e.g., to ensure good hydration, to assist in the organization of the extracellular matrix, to act as a filler material; and to participate in tissue repair mechanisms. However, with age, the quantity of hyaluronan, collagen, elastin, and other matrix polymers present in the skin decreases. For example, repeated exposed to ultra violet light, e.g., from the sun, causes dermal cells to both decrease their production of hyaluronan as well as increase the rate of its degradation. This hyaluronan loss results in various skin conditions such as, e.g., imperfects, defects, diseases and/or disorders, and the like. For instance, there is a strong correlation between the water content in the skin and levels of hyaluronan in the dermal tissue. As skin ages, the amount and quality of hyaluronan in the skin is reduced. These changes lead to drying and wrinkling of the skin.
Dermal fillers are useful in treating soft tissue condition and in other skin therapies because the fillers can replace lost endogenous matrix polymers, or enhance/facilitate the function of existing matrix polymers, in order to treat these skin conditions. In the past, such compositions have been used in cosmetic applications to fill wrinkles, lines, folds, scars, and to enhance dermal tissue, such as, e.g., to plump thin lips, or fill-in sunken eyes or shallow cheeks. One common matrix polymer used in dermal filler compositions is hyaluronan. Because hyaluronan is natural to the human body, it is a generally well tolerated and a fairly low risk treatment for a wide variety of skin conditions.
Originally, compositions comprising hyaluronan where made from naturally-occurring polymers, which exist in an uncrosslinked state. Although exhibiting excellent biocompatibility and affinity for water molecules, naturally-occurring hyaluronan exhibits poor biomechanical properties as a dermal filler. One primary reason is that because this polymer is uncrosslinked, it is highly soluble and, as such, is cleared rapidly when administered into a skin region. This in vivo clearance is primarily achieved by rapid degradation of the polymers, principally enzymatic degradation via hyaluronidase and chemical degradation via free-radicals. Thus, while still in commercial use, compositions comprising uncrosslinked hyaluronan polymers tend to degrade within a few days after administration and thus require fairly frequent reinjection to maintain their skin improving effect.
To minimize the effect of these in vivo degradation pathways, matrix polymers are crosslinked to one another to form a stabilized hydrogel. Because hydrogels comprising crosslinked matrix polymers are a more solid substance, dermal fillers comprising such hydrogels remain in place at the implant site longer. In addition, these hydrogels are more suitable as a dermal filler because the more solid nature thereof improves the mechanical properties of the filler, allowing the filler to better lift and fill a skin region. Hyaluronan polymers are typically crosslinked with a crosslinking agent to form covalent bonds between hyaluronan polymers. Such crosslinked polymers form a less water soluble hydrogel network that is more resistant to degradation, and thus requires less frequent reinjection, than the non-crosslinked hyaluronan compositions.
Vitamin C, also known as ascorbic acid or AsA, is well known as an antioxidant which reduces, and thereby neutralizes, reactive oxygen species such as hydrogen peroxide, thus reducing oxidative stress for various clinical benefits, including treating cardiovascular disease, hypertension, chronic inflammatory diseases, diabetes, and conditions with severe burns. For example, among other benefits, vitamin C acts as an anti-inflammatory, and promotes collagenesis and angiogenesis. Vitamin C is known to promote collagenesis and/or angiogenesis by functioning as a cofactor in enzymatic reactions to promote collagen formation, develop and maintain blood vessels and cartilage. Vitamin C is known to inhibit biological functions of tyrosinase to prevent melanin formation or lightening melanin pigmentation. For these reasons, there is interest in developing dermal filler compositions containing vitamin C.
Vitamin C is generally unstable upon exposure to air, light and heat. It is also considered cytotoxic at certain levels. When vitamin C is physically mixed with hyaluronic acid gel and injected into the skin, the vitamin C is fully released from the mixture in less than one week.
It would be desirable to provide an injectable hyaluronic acid-based composition with vitamin C, or another vitamin, having a sustained release rate, that is, a release rate over weeks or even months rather than a few days. However, it has proven difficult to develop stable, effective, sustained release dermal filler products which include vitamins. The present invention provides improved hyaluronic acid-based dermal filler compositions including conjugated vitamins, for example, vitamin derivatives.